Many vehicle seats of the type wherein the seat cushion thereof can be folded upwardly are widely used as a rear seat including a second seat or a third seat. In this sort of seat, the seat cushion has its front end portion swingably connected to a floor of vehicle by a connecting means. Such connecting means for example includes a substantially “U” shaped connecting rod formed by bending a rod-like element into a substantially “U” shape, or has left and right connecting links. Hence, the seat cushion is arranged on the floor of the vehicle such that a rear end of the seat is movable upwardly relative to the front end portion thereof, whereas a seat back of the seat is arranged above the floor of vehicle so as to be foldable forwardly and downwardly. (See Japanese Laid-Open Patent Publications Nos. 2009-255718 and 2007-191120, for instance) With this seat arrangement, the seat cushion is first folded upwardly to a vertically folded position and thereafter the seat back is folded forwardly and downwardly to a substantially horizontal position, providing a luggage space over a rear surface of the thus-folded seat back. In this mode of prior art, both the seat cushion and the seat back are directly mounted on the floor of vehicle There is also a known seat of this kind in which the seat cushion and the seat back are not directly mounted on the vehicle floor, but are disposed on a base element (support base) which is provided on the floor of vehicle.
The seat cushion is normally retained in a substantially horizontal use position where a seat occupant may sit thereon. Then a rear end of the seat cushion is located below a lower end of the seat back so as to be in close contact with and restrained by that lower end of the seat back, to the extent that no clearance exists between those seat cushion's rear end and seat back's lower end. Further, there is an engagement means between the rear end of the seat cushion and the lower end of the seat back. The engagement means is adapted for engaging the rear end of the seat cushion with the lower end of the seat back for the purpose of retaining the seat cushion at the use position where a seat occupant may sit thereon.
Now, described is how the seat cushion is folded upwardly. First, the seat cushion is moved upwardly in a swinging manner under the action of the aforesaid connecting means, so that the front end of the seat cushion is displaced upwardly, whereas the rear end thereof is drawn to the outside from below the lower end of the seat back, while it is being moved downwardly. Then, a disengagement operation is prepared to disengage the rear end of the seat cushion from the lower end of the seat back, and to thereby release a restrained state where the rear end of seat cushion is restrained by the lower end of seat back. Subsequently, while temporarily raising the front end portion of the seat cushion, the seat cushion is swingingly moved by approx. 90 degrees upwards under the action of the connecting means. As a result, the rear end of the seat cushion is displaced upwardly to a point corresponding to a vertically folded position, where the seat cushion is folded and stands substantially perpendicular to the floor of vehicle.
To return the seat cushion from the vertically folded position to the use position, at which a seat occupant may sit thereon, the seat back is returned to its upright home position, and thereafter the seat cushion is unfolded downwards in order that its rear end is slidingly brought to a location below the lower end of so vertically-set seat back, which is followed by an engagement operation for engaging the rear end of the seat cushion with the lower end of the seat back.
An engagement means for engaging the rear end of the seat cushion with the lower end of the seat back to retain the seat cushion at the above-said use position thereof, is shown for example, in Laid-Open Japanese Patent Publication No. 2009-255718. That shows an engagement means which comprises an engagement piece having a substantially “U” shape as viewed in plan. The engagement piece is formed by bending a wire into the substantially “U” shape and is provided to a rear end of a seat frame. The engagement piece is formed by combination of a plurality of wires (steel wires), such that the engagement piece projects in a direction rearwardly of the seat frame. A retainer member provided to a connecting rod is extended between left and right side frame members provided in the seat cushion. With this arrangement, the engagement piece is engaged with the retainer member. In another example, Japanese Laid-Open Publication No. 2007-191120 shows an engagement means, in which, a protruding portion defined in an upper area of a rear end of a seat cushion is engaged with a recessed portion defined in a rear end of a seat back.